“pMDIs” are well known in the art of inhalation devices. It is therefore not necessary to describe the construction and operation of a pMDI other than in bare essentials.
A pMDI comprises an aerosol canister and a tubular actuator.
The aerosol canister comprises a pressurised can, typically made from a metal, such as aluminium. Inside the can there is contained the pressurised medicinal aerosol formulation. The can is sealingly capped by a metering valve assembly at what will hereinafter be referred to as the “outlet end” of the aerosol canister. The valve assembly includes a hollow dispensing member or valve stem which projects from the outlet end of the aerosol canister. The dispensing member is mounted for sliding movement relative to the aerosol canister between an extended position, to which the dispensing member is biased by a biasing mechanism in the valve assembly, and a depressed position.
Movement of the dispensing member from the extended position to the depressed position results in a metered dose of the aerosol formulation being dispensed from the canister through the dispensing member.
The tubular actuator comprises an internal passageway having an open end. The aerosol canister is slidable into the internal passageway through the open end with the outlet end being inserted first into the internal passageway.
The actuator has a stand or stem block which receives the dispensing member of the aerosol canister when the aerosol canister is received in the actuator in a “rest position”. The stand has a passageway with an inlet end for receiving the dispensing member and an outlet end which faces a mouthpiece of the actuator. The stand holds the dispensing member stationary in the actuator whereby depression of the aerosol canister from its rest position farther into the actuator to an “actuated position” causes the dispensing member to be displaced from the extended position to the depressed position relative to the canister. A metered dose of the aerosol formulation will thereby be dispensed out of the mouthpiece of the actuator via the internal passageway of the stand.
In use, a patient in need of a metered dose of the medicinal aerosol formulation places their lips on the mouthpiece of the actuator and then concurrently inhales and depresses the aerosol canister from the rest position to the actuated position. The inspiratory airflow produced by the patient entrains the medicinal component of the aerosol into the patient's respiratory tract.
Instead of a mouthpiece, there could be provided a nozzle for nasal use.
Developments to these pMDIs have included the provision of actuation indicators therefor, for instance dose counters which are either incremented on each actuation of the PMDI to display a running total of the number of doses dispensed from the PMDI or decremented on each actuation to display the number of doses left in the dispenser. See, for example, WO96/16686, U.S. Pat. No. 4,817,822 and U.S. Pat. No. 5,482,030.
A recently developed dose counter is described in PCT Patent Application No. WO98/56444, to Glaxo Group Limited, the entire contents of which are incorporated herein by way of reference. The dose counter is fixably secured on the outlet end of the aerosol canister and includes a display which denotes the number of metered doses of the medicament formulation left in the aerosol canister. The display of the dose counter is visible to the patient through a window provided in the actuator. The display is presented by a plurality of indicator wheels rotatably mounted on a common axle, each wheel having numerals from ‘0’ to ‘9’ displayed in series around the circumference.
Before the dose counter is mounted on the aerosol canister, the display wheels are arranged so that the display shows the claimed total number of doses available in the aerosol canister, the so-called “label claim”. Upon each actuation, an indexing mechanism in the dose counter comprising a star wheel, a driver yoke and a rack operates to decrement the number displayed by the display by rotation of one or more of the indicator wheels.
When the aerosol canister with attached dose counter is in a rest position in the actuator, the rack, which is formed in the actuator, protrudes into the dose counter. When the aerosol canister is moved from the rest position to the actuated position, this results in relative movement between the dose counter and the rack. During this relative movement, the rack engages the yoke of the indexing mechanism to cause it to operate to decrement the number displayed by the display by turning the star wheel.
The index mechanism of the mechanical dose counter known from WO98/56444 includes a lost motion coupling to compensate for overtravel of the dose counter relative to the rack as the aerosol canister reciprocates between the rest position and the actuated position in the actuator.
A device and method for attaching a dose counter to an aerosol canister is disclosed in PCT application publication WO01/28887, also to Glaxo Group Limited, the entire contents of which are incorporated herein by way of reference. The dose counter is fixedly secured to the outlet end of the aerosol canister through a split-ring collar. More particularly, a skirt portion of the dose counter housing surrounds a neck on the can of the aerosol canister, and the split-ring collar is wedged in-between the skirt and a re-entrant surface of the neck and then ultrasonically welded to the skirt. This effectively provides a permanent connection between the dose counter and the aerosol canister to prevent the dose counter from being tampered with.
All these prior art devices, however, require the components thereof to be manufactured to tight tolerances so that they correctly function, or they are difficult to assemble. Accordingly, they are relatively expensive to manufacture. Further, they are unsuitable for attachment to canisters or actuators that are made with wide manufacturing tolerances, as may occur when attempting to reduce the manufacturing cost of actuators or aerosol canisters.
It would be desirable to provide an actuator and/or dose counter that is inexpensive to manufacture due to the lack of the need for tight manufacturing tolerances. It would also be desirable to provide an actuator and/or dose counter that is simple and therefore inexpensive to assemble. It would also be desirable to provide an actuator and/or dose counter that can be used with more than one size of aerosol canister. It would also be desirable to provide components of such devices that allow for wide manufacturing tolerances.